Avionics - Satellite Communication Quiz(MCQ)
A)
Fall back
B)
Continue to orbit the earth
C)
Stays where it was released
D)
Overshoots the altitude and moves at a constant speed

Explanation : If a satellite were launched vertically from the earth and then released, it would fall back to earth because of gravity. For the satellite to go into orbit around the earth, it must have some forward motion. For that reason, when the satellite is launched, it is given both vertical and forward motion.

A)
Consume less fuel
B)
Most efficient geometry
C)
Better coverage on earth
D)
Position can be easily determined

Correct Answer :   Position can be easily determined

Explanation : A satellite rotates about the earth in either a circular or an elliptical path. Circles and ellipses are geometric figures that can be accurately described mathematically. Because the orbit is either circular or elliptical, it is possible to calculate the position of a satellite at any given time.

A)
Perigee
B)
Apogee
C)
D)

Explanation : The direction of satellite rotation may be either in the same direction as the earth’s rotation or against the direction of earth’s rotation. In the former case, the orbit is said to be posigrade, and in the latter case, retrograde. Most orbits are posigrade.

A)
Apogee
B)
Perigee
C)
D)

Explanation : In an elliptical orbit, the speed changes depending upon the height of the satellite above the earth. Naturally, the speed of the satellite is greater when it is close to the earth than when it is far away. The closest point is called the perigee.

A)
Time period
B)
Sidereal period
C)
Lapsed time
D)
Unit frequency

Explanation : The period is the time it takes for a satellite to complete one orbit. It is also called the sidereal period. A sidereal orbit uses some external fixed or apparently motionless object such as the sun or star for reference in determining a sidereal period.

A)
Subsatellite point
B)
C)
Satellite point
D)
Supersatellite point

Explanation : The satellite location is specified by a point on the surface of the earth directly below the satellite. This point is known as the subsatellite point (SSP). The subsatellite point is then located by using conventional latitude and longitude designations.

A)
20
B)
40
C)
50
D)
70

Explanation : Most communication satellites in use today are of the geosynchronous variety. Approximately 40 percent of the earth’s surface can be “seen” or accessed from such a satellite. Users inside that area can use the satellite for communication.

A)
Time period
B)
Lapsed time
C)
Synodic period
D)
Sidereal period

Explanation : Another method of expressing the time for one orbit is the revolution or synodic period. One revolution (1 r) is the period of time that elapses between the successive passes of the satellite over a given meridian of earth longitude. Naturally, the synodic and sidereal periods differ from each other because of the earth’s rotation.

A)
Circular orbit
B)
Elliptical orbit
C)
Triangular orbit
D)
Geosynchronous orbit

Explanation : The best solution is to launch a synchronous or geostationary satellite. In a geosynchronous earth orbit. Since the satellite remains apparently fixed, no special earth station tracking antennas are required. The antenna is simply pointed at the satellite and remains in a fixed position. With this arrangement, continuous communication is possible.

A)
Relay satellites
B)
Repeater satellites
C)
Communication satellites
D)
Geosynchronous satellites

Explanation : Communication satellites are not originators of information to be transmitted. If a transmitting station cannot communicate directly with one or more receiving stations because of line-of-sight restrictions, a satellite can be used. The transmitting station sends the information to the satellite, which in turn re-transmits it to the receiving stations.

A)
Transponder
B)
Relay
C)
Repeater
D)
Duplexer

Explanation : The transmitter-receiver combination in the satellite is known as a transponder. The basic functions of a transponder are amplification and frequency translation. The reason for frequency translation is that the transponder cannot transmit and receive on the same frequency.

A)
More gain
B)
Redundancy
C)
Better reception
D)
More number of operating channel

Correct Answer :   More number of operating channel

Explanation : To be economically feasible, a satellite must be capable of handling several channels. As a result, most satellites contain multiple transponders, each operating at a different frequency. Each transponder represents an individual communication channel.

A)
More bandwidth
B)
Are not diffracted by the ionosphere
C)
Economically viable
D)
More spectrum space

Correct Answer :   Are not diffracted by the ionosphere

Explanation : VHF, UHF, and microwave signals penetrate the ionosphere with little or no attenuation and are not refracted to earth. Lower frequencies undergo total internal refraction and get reflected back to earth.

A)
More bandwidth
B)
Overcrowding
C)
Lesser attenuation
D)
Less power requirements

Explanation : Most new communication satellites will operate in the Ku band. This upward shift in frequency is happening because the C band is overcrowded. Many communication satellites are in orbit now, most of them operating in the C band. However, there is some difficulty with interference because of the heavy usage. The only way this interference will be minimized is to shift all future satellite communication to higher frequencies.

A)
Multiplexing
B)
Modulation
C)
Spatial isolation
D)
Frequency reuse

Explanation : By using narrow beam or spot beam antennas, the area on the earth covered by the satellite can be divided up into smaller segments. Earth stations in each segment may actually use the same frequency, but because of the very narrow beam widths of the antennas, there is no interference between adjacent segments.

A)
Frequency reuse
B)
Modulation
C)
Multiplexing
D)
Spatial isolation

Explanation : In the frequency reuse technique two systems use the same frequency, although operating on exactly the same frequencies, they are isolated from each other by the use of special antenna techniques. For example, a vertically polarized antenna will not respond to a horizontally polarized signal and vice versa. Or a left-hand circularly polarized (LHCP) antenna will not respond to a right-hand circularly polarized (RHCP) signal and vice versa.

A)
More gain
B)
High speed
C)
Error detection
D)

Explanation : At times there is more traffic than there are transponders to handle it. For that reason, numerous techniques have been developed to effectively increase the bandwidth and signal-carrying capacity of the satellite. Two of these techniques are known as frequency reuse and spatial isolation.

A)
12Mpbs
B)
32Mpbs
C)
36Mpbs
D)
72Mpbs

Explanation : For binary transmission, the maximum theoretical data rate or channel capacity C for a given bandwidth B is C = 2B = 2(36) =72Mpbs.

A)
Power system
B)
Ground station
C)
Telemetry tracking
D)
Communication subsystem

Explanation : The communication subsystem is the most important part of the satellite. It requires varies additional systems like the power system, propulsion system, telemetry system for its proper functioning. The ground system however is not one of the satellite subsystem and is independent of the satellite. It is just a transponder to monitor and command the satellite.

A)
AKM
B)
Jet thruster
C)
Gyroscope
D)
Fuel control system

Explanation : The propulsion subsystem consists of the AKM(Apogee kick motor), jet thruster and the fuel control system. Gyroscopes and other attitude systems fall under the attitude control subsystem.

A)
Computer data
B)
C)
Voice, video, computer data
D)

Correct Answer :   Voice, video, computer data

Explanation : An earth station takes the signals to be transmitted, known as baseband signals, and modulates a microwave carrier. The three most common baseband signals are voice, video, and computer data.

A)
Transponder
B)
Relay
C)
Repeater
D)
Transducer

Explanation : The uplink signals from earth are amplified, translated in frequency, and re-transmitted on the downlink to one or more earth stations. The component that performs this function is known as a transponder.

A)
Heavy attenuation
B)
Economically not profitable
C)
Weight of the system increases five fold
D)
High power output over wideband is not possible

Correct Answer :   High power output over wideband is not possible

Explanation : it is generally not possible to generate very high output power over such wide bandwidth. The fact is that no components and circuits can do this well. The high-power amplifiers in most transponders are traveling-wave tubes that inherently have limited bandwidth. They operate well over a small range but cannot deal with the entire 500-MHz bandwidth allocated to a satellite.

A)
Dual mixer transponder
B)
Dual conversion transponders
C)
Regenerative transponders
D)
Single conversion transponders

Correct Answer :   Dual conversion transponders

Explanation : A dual-conversion transponder makes the frequency translation in two steps with two mixers. No demodulation occurs.

A)
Less attenuation
B)
Reduce interference
C)
Maximum efficiency
D)
To reduce space occupied by filters

Explanation : Because of the close proximity of the transmitter and the receiver in the satellite, the high transmitter output power for the downlink is picked up by that satellite receiver. Naturally, the uplink signal is totally obliterated. Furthermore, the transmitter output fed back into the receiver input causes oscillation. To avoid this problem, the receiver and transmitter in the satellite transponder are designed to operate at separate frequencies. In this way, they will not interfere with each other.

A)
Reduces noise
B)
Increases antenna gain
C)
D)
To reduce it to an intermediate frequency

Explanation : The diplexer feeds a bandpass filter (BPF) in the receiver section that ensures that only the received frequencies pass through to the sensitive receiving circuits. This bandpass filter blocks the high-power transmit a signal that can occur simultaneously with reception. This prevents overload and damage to the receiver.

A)
Frequency synthesizer
B)
Quartz oscillator
C)
Electric oscillators
D)
Magnetic oscillator

Explanation : In RF tuning, the first local oscillator is made adjustable. Generally, a frequency synthesizer is used in this application. The frequency synthesizer generates a highly stable signal at selected frequency increments.

A)
RF amplifiers
B)
Buffer amplifiers
C)
Klystron amplifier
D)
Operational amplifiers

Explanation : The signals to be sent to the satellite might be TV programs, multiple telephone calls, or digital data from a computer. These signals are used to modulate the carrier, which is then amplified by a large traveling-wave tube or klystron amplifier.

A)
Mixer
B)
Antenna
C)
Power amplifiers
D)
Up converter

Explanation : The transmit subsystem consists of two basic parts, the up converters and the power amplifiers. The up converters translate the baseband signals modulated on to carriers up to the final uplink microwave frequencies.

A)
Quartz oscillator
B)
RF frequency synthesizer
C)
Magnetic oscillator
D)
Fixed-frequency local oscillator

Correct Answer :   RF frequency synthesizer

Explanation : In RF tuning, a mixer fed by a fixed-frequency local oscillator performs an initial up conversion to 700 MHz. Then a sophisticated RF frequency synthesizer applied to a second mixer provides up conversion to the final microwave frequency.

A)
Mixer
B)
Microwave combiner
C)
Amplifier
D)
Multiplexer

Explanation : Individual up converters are used on each modulated channel. At the output of the up converters, all the signals are combined in a microwave combiner, which produces a single output signal that is fed to the final amplifiers.

A)
GPS
B)
Research
C)
Surveillance
D)
Telephone service

Explanation : The primary use of communication satellites is in long-distance telephone service. Satellites greatly simplify long-distance calls not only within countries but also worldwide.

A)
Power requirements
B)
Economically feasible
C)
High frequency signal
D)
Long distance communication

Explanation : TV signals are being transmitted through satellites for redistribution. Because of the very high-frequency signals involved in TV transmission, other long-distance transmission methods are not technically or economically feasible.

A)
Fixed satellite service
B)
Mobile satellite service
C)
D)

Explanation : The direct broadcast satellite (DBS) system is an all-digital system. Data compression techniques are used to reduce the data rate in order to produce high-quality picture and sound. They uses special broad coverage satellites with high power to transmit cable-TV-like services direct to homes equipped with the special DBS receivers.

A)
C band
B)
X band
C)
Ku band
D)
MF band

Explanation : The DBS satellite uses the Ku band with a frequency range of 11 to 14 GHz. Uplink signals are usually in the 14- to 14.5-GHz range, and the downlink usually covers the range of 10.95 to 12.75 GHz.

A)
Modulation
B)
Frequency reuse
C)
Multiplexing
D)
Spatial isolation

Explanation : The digital signal is transmitted from the satellite to the receivers using circular polarization. The DBS satellites have right-hand and left-hand circularly polarized (RHCP and LHCP) helical antennas. By transmitting both polarities of signal, frequency reuse can be incorporated to double the channel capacity.

A)
72
B)
66
C)
51
D)
32

Explanation : The satellite systems use low-earth-orbit satellites to perform the relay services to the main telephone system or to make a connection directly between any two cellular telephones using the system. One of the oldest and most widely used is the Iridium system. It uses a constellation of 66 satellites in six polar orbits with 11 satellites per orbit 420 mi above the earth.

A)
Up converter
B)
Power driver circuit
C)
Operational amplifier
D)
Intermediate-power amplifier

Explanation : The power amplifier usually begins with an initial stage called the intermediate-power amplifier (IPA). This provides sufficient drive to the final high-power amplifier (HPA).

A)
Ka band
B)
L band
C)
C band
D)
Ku band